Method for manufacturing CMOS image sensor
Disclosed is a CMOS image sensor and a method for manufacturing a CMOS image sensor. The method includes: (a) forming a resist film on a semiconductor substrate comprising a light sensing part, a protecting layer over the light sensing part, and an exposed bonding pad; (b) forming a color filter array on the thin resist film; (c) forming a plurality of microlenses over the color filter array; and (d) etching the resultant structure until the bonding pad is exposed.
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1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more specifically, to a method for manufacturing a complementary metal oxide semiconductor (CMOS) image sensor.
2. Description of the Related Art
An image sensor, as a kind of semiconductor device, transforms optical images into electrical signals. Image sensors can be generally classified into charge coupled devices (CCDs) and CMOS image sensors. Among these image sensors, a CMOS image sensor comprises a photo diode for detecting incident light and transforming it into electrical signals, and logic circuits for transmitting and processing the electrical signals.
In processes for manufacturing a CMOS image sensor, it is desired to increase a so-called fill factor, defined as a ratio of light sensing area to total image sensor area, for the purpose of improving light sensitivity. However, since the light sensing part is formed only in an area other than the area where logic circuits are formed, there are limits to improving the fill factor of the device. For such reason, forming a plurality of microlenses on or over color filters of a CMOS image sensor has been widely employed as one alternative light condensing technique for changing a path of light incident on regions other than the light sensing part and concentrating light to the light sensing part.
A conventional method for manufacturing a CMOS image sensor including microlenses is hereinafter described referring to
A conventional CMOS image sensor comprises: a light sensing part 13 including a photo diode 11 for accepting incident light, and for generating and accumulating electric charges; a protecting layer 21 formed on a structure of the light sensing part; color filter arrays 23; a planarization layer 25; and a plurality of microlenses 27.
In a conventional method of manufacturing such structured CMOS image sensor, as shown in
Next, as shown in
Then, as shown in
Next, a photoresist layer is applied, exposed, and developed on the planarization layer 25, thus forming a plurality of photoresist patterns. These photoresist patterns are thermally reflowed and cured to form a lens, thus resulting in a plurality of microlenses 27 shown in
According to the above-described conventional method, the remaining photoresist material in the bond pad opening process is ashed by a reactive ion etch. Thus, surface properties of the protecting layer 21 can be locally changed according to the conditions (ambient and other) in the ashing process. As a result, adhesion of color photoresist on the protecting layer 21 may deteriorate so that some of the patterned color filters peel off. In general, the color filter array 23 is formed of organic materials. Especially, in the case where the color photoresist contains a large amount of pigment, the peeling phenomenon may occur more frequently because of relatively large-sized pigment particles affecting adhesion to the protecting layer 21. There is a need in the art to solve the peeling problems of the color filters because it can induce deterioration and/or failure of certain characteristics of the device (e.g., discoloration).
In the case where the peeling phenomenon occurs, the color filter array 23 and microlenses 27 may be reworked and reproduced by stripping one or more of the color filter array 23, the planarization layer 25, and the microlenses 27, and repeating the photolithography process(es) for the color filter array 23, the planarization layer 25, and the microlenses 27, up to several times. However, a developing solution used in the photolithography process generally comprises TMAH ((Tetramethylammonium hydroxide) which erodes the exposed wiring bonding pad 15. Therefore, the number of repetitions of the stripping and photolithography process is restricted. Moreover, several repetitions of the photolithography process can lead to contamination of wiring bonding pad 15, thus resulting in a wiring failure.
Meanwhile, according to the conventional method, the microlenses 27 are formed distant from each other by about 0.2 μm˜0.5 μm, for the purpose of preventing formation of bridges between the microlenses 27 during the curing and reflowing processes of the corresponding photoresist pattern. However, the gap between microlenses 27 results in at least some loss of the light incident between microlenses 27, and especially a problem that the resolution of color signals may be less than optimal due to oblique light incident to adjacent pixels.
SUMMARY OF THE INVENTIONIt is, therefore, an object of the present invention to provide a method for manufacturing a CMOS image sensor, wherein a bonding pad is protected by a thin resist film before formation of a color filter array, and the thin resist film covering the bonding pad is removed after formation of microlenses, thus inhibiting, suppressing or preventing the color filter array from peeling off.
Another object of the present invention is to provide a method for manufacturing a CMOS image sensor, in which unnecessary gaps between microlenses are reduced, minimized or eliminated, thereby improving the light condensing efficiency of the image sensor, and reducing or preventing adverse effects of oblique light incident to adjacent pixels, and ultimately enabling realization of more vivid colors.
It is still another object of the present invention to provide a method for manufacturing a CMOS image sensor having improved light sensitivity by improving the shape uniformity of the microlenses.
To achieve the above objects, an embodiment of a method for manufacturing a CMOS image sensor according to the present invention comprises the steps of: (a) forming a resist film on a semiconductor substrate comprising a light sensing part, a protecting layer over the light sensing part, and an exposed bonding pad; (b) forming a color filter array on the resist film; (c) forming a plurality of microlenses over the color filter array; and (d) etching the resultant structure until the bonding pad is exposed again.
Alternatively, a method for manufacturing a CMOS image sensor according to the present, can comprise the steps of: forming an organic material layer over an entire surface of the substrate, including a plurality of microlenses and a bonding pad; and etching the resultant structure until the bonding pad is exposed.
These and other aspects of the invention will become evident by reference to the following description of the invention, often referring to the accompanying drawings.
Hereinafter, one embodiment of a manufacturing method for a CMOS image sensor according to the present invention will be described with reference to
Referring to
Next, as shown in
Thereafter, as shown in
As shown in
Next, a photoresist layer is applied, exposed, and developed on the planarization layer 205, thus forming a photoresist pattern (e.g., a plurality of microlens bodies). The photoresist pattern is bleached, thermally reflowed and cured to form lenses having a desired curvature, thus resulting in a plurality of microlenses 207 as shown in
Here, the number of microlenses 207 preferably relates to the number of pixels in the image sensor, and they have a size (e.g., area) as large as possible, in order to improve light sensitivity and condensing efficiency to incident light. However, it is difficult to uniformly fabricate so many (relatively) large microlenses because of morphology effects due to the underlying layer and photo effects in the microlenses. Therefore, gaps (e.g., 303) between the microlenses 207 should be formed to the extent that they can be controlled appropriately (e.g., reproduced within manufacturing tolerances or limits), as shown in
Next, the substrate is etched (e.g., it undergoes a blank etch) using an oxygen (O2) plasma or other plasma comprising an oxygen atom source (e.g., O3, N2O, NO, CO2, etc., which may further contain a carrier gas or noble gas such as N2, Ar, He, etc.) so that the portion of the resist film 202 covering the bonding pad 105 is removed, and simultaneously, the microlenses 207 may be etched. In this process, irregular tails (or “bridges”) between microlenses 207 may also be removed, and gaps 303 between microlenses 207 may be shallow etched. Especially, regions 303 between microlenses 207 may be etched to in the form of a concave lens, thus resulting in “gapless” microlenses, as shown in
Meanwhile, referring to
As shown in
According to the present invention, a resist film for protecting the bonding pad is formed over the bonding pads before forming the color filters and removed from the bonding pads after forming the microlenses, which enables a reduction and/or prevention of erosion of the bonding pad, as well as a change in surface properties of the protecting layer. As a result, the peeling phenomenon of the color filter array can be prevented. In addition, the present invention enables (a) improvement in shape uniformity of the microlenses and (b) formation of gapless microlenses. Moreover, the present invention has such advantages that the size of microlens can be maximized, thus the light sensitivity can be improved. Especially, using the organic material layer facilitates formation of a concave profile between microlenses.
While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims
1. A method for manufacturing a CMOS image sensor, comprising the steps of:
- (a) forming a resist film on a protecting layer over a light sensing part of a semiconductor substrate and on an exposed bonding pad;
- (b) forming a color filter array on the resist film;
- (c) forming a planarization layer on the color filter array;
- (d) forming a plurality of microlenses on the planarization layer; and
- (e) after forming the plurality of microlenses, etching the planarization layer and the resist film on the bonding pad until the bonding pad is exposed, all microlens material is removed between adjacent microlenses, and a concave profile is formed in the planarization layer between adjacent microlenses.
2. The method of claim 1, wherein the resist film comprises an organic material.
3. The method of claim 2, wherein the resist film has at least a predetermined transparency to visible light.
4. The method of claim 1, wherein the resist film comprises a thermosetting resin.
5. The method of claim 1, wherein the resist film comprises an acrylic resin.
6. The method of claim 1, wherein the resist film has a thickness not more than 50 nm.
7. The method of claim 1, wherein the etching step removes the resist film covering the bonding pad and forms a gap between the microlenses.
8. The method of claim 1, wherein the etching step comprises etching with a plasma comprising an oxygen source.
9. The method of claim 8, wherein the oxygen source comprises O2.
10. The method of claim 1, wherein the microlenses comprise a second resist material, and etching the resist film simultaneously etches the microlenses until the concave profile is formed in the planarization layer.
11. The method of claim 1, further comprising, before the etching step, forming an organic material layer over an entire surface of the substrate including the plurality of microlenses, and wherein etching the planarization layer and the resist film further comprises simultaneously etching the organic material layer.
12. A method for manufacturing a CMOS image sensor, comprising the steps of:
- (a) forming a resist film on a protecting layer over a light sensing part of a semiconductor substrate and on an exposed bonding pad;
- (b) forming a color filter array on the resist film;
- (c) forming a planarization layer on the color filter array;
- (d) forming a plurality of microlenses on the planarization layer, wherein adjacent microlenses have a space therebetween exposing regions of the planarization layer;
- (e) forming an organic material layer over an entire surface of the substrate including the plurality of microlenses; and
- (f) etching the organic material layer and the protecting layer on the bonding pad until the bonding pad is exposed and a concave profile is formed in the organic material layer and the planarization layer between adjacent microlenses.
13. The method of claim 12, wherein the organic material layer comprises a photoresist or a thermosetting resin.
14. The method of claim 12, wherein the organic material layer has a thickness of 30 nm˜100 nm.
15. The method of claim 12, wherein the resist film comprises an organic material or a thermosetting resin having a predetermined transparency to visible light.
16. The method of claim 12, wherein the etching step removes the organic material layer and the resist film covering the bonding pad, and forms a gap between the micro lenses.
17. The method of claim 12, wherein the etching step utilizes a plasma comprising oxygen.
18. The method of claim 12, comprising the step of irradiating the plurality of microlenses with ultraviolet light before forming the organic material layer.
19. The method of claim 12, wherein the organic material layer comprises a second resist material, and etching the protecting layer simultaneously etches the microlenses until the concave profile is formed in the organic material layer.
5621461 | April 15, 1997 | Higashide |
5902704 | May 11, 1999 | Schoenborn et al. |
6069350 | May 30, 2000 | Ohtsuka et al. |
6632700 | October 14, 2003 | Fan et al. |
6656762 | December 2, 2003 | Kim |
6794215 | September 21, 2004 | Park et al. |
6861280 | March 1, 2005 | Yamamoto |
7268009 | September 11, 2007 | Hwang |
20030176010 | September 18, 2003 | Kim |
1445816 | October 2003 | CN |
1531100 | September 2004 | CN |
06-112459 | April 1994 | JP |
- People's Republic of China Office Action; Application No. 2006-10090550.2; Dated: Dec. 7, 2007; State Intellectual Property Office of People's Republic of China; People's Republic of China.
- Takahisa, Ueno; On-Chip Lens and Manufacture Thereof; Patent Abstracts of Japan; Publication No. 06-112459; Publication Date: Apr. 22, 1994; Japan.
- Huawei Semiconductor Co., Ltd.; Image Sensor for Microlens with Integrated Filter Layer and Producing Method Thereof; SIPO Patent Search Engine; Publication No. 1531100 (Abstract Only); Publication Date: Sep. 22, 2004; State Intellectual Property Office of the People's Republic of China; People's Republic of China.
- Kim, Chae-Gap; Method for Manufacturing Semiconductor Device Suitable for Image Sensor; SIPO Patent Search Engine; Publication No. 1445816 (Abstract Only); Publication Date: Oct. 1, 2003; State Intellectual Property Office of the People's Republic of China; People's Republic of China.
Type: Grant
Filed: Jun 26, 2006
Date of Patent: Mar 16, 2010
Patent Publication Number: 20060292734
Assignee: Dongbu Electronics Co., Ltd. (Seoul)
Inventor: Sang Sik Kim (Suwon-si)
Primary Examiner: Khiem D Nguyen
Attorney: The Law Offices of Andrew D. Fortney
Application Number: 11/476,223
International Classification: H01L 21/00 (20060101);